The main practical difference is that if you use a process for isolation, the OS will garbage collect all process resources on termination (memory, file descrip

The main practical difference is that if you use a process for isolation, the OS will garbage collect all process resources on termination (memory, file descriptors, threads, mutexes, etc.). If you are using a thread, you better not be leaking anything. Otherwise you are "ulimits" resources away from putting your "main" process into a crashing loop, e.g., if you leak 1 file-descriptor per crash, then you can crash your thread < 1000 times. Performance-wise, you are probably worse with threads as well. On linux, you can initialize a web-server on your main process, and spawn new processes by forking it. Forking isn't only pretty much instantaneous, your child process is initialized with the same state as the parent, so you instantaneously get a fully initialized web server (e.g. with multiple threads already started in your task pool, etc.).